National Teacher Enhancement Project

Middle School Home Energy Audit

MEASURING ENERGY USAGE


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Energy Use of Home Appliances

How much electricity do our appliances use? You can usually find the wattage of most appliances on the nameplate on the back or bottom of the appliance. The wattage listed is the maximum power drawn by the appliance. Wattage = current X voltage. Often you will see the letters UL on the nameplate, which means the product has been tested to safety standards. Adjusting volume or changing settings can affect the actual amount of power consumed. Many appliances draw small amounts of power even when they are turned off. These "phantom loads" occur in VCR's, televisions, stereos, computers and increase the appliance's energy consumption a few watts per hour. Below is a list of some common household items and the wattage used for each.

 
 

 APPLIANCE

WATTAGE 

  APPLIANCE

 WATTAGE

 clock radio

 10

 coffee maker

  900-1200
clothes washer

  350-500

 clothes dryer

 1800-5000

 dishwasher

 1200-2400

 ceiling fan

 65-175

 hair dryer

 1200-1875

 clothes iron

 1000-1800
 microwave   750-1100  refrigerator 1725

computer: CPU

120

 VCR/DVD

17-21/20-25

Computer: Monitor

150

 19" color television

 110

 stereo

  400

 water bed

 120-380
 
Now let's calculate the annual cost to run an appliance for a year.
 
 
Multiply this number by your local utility's rate per kWh consumed (In Denver the cost is 8.9 cents/kWh) to calculate annual cost.
 
 
 

EXAMPLE
If John uses a window fan (200 watts) 4 hours a day for 120 days per year, how much does it cost him to run his fan per year?
 
200 X 4 X 120 = 96 kWh
1000
 
96 kWh X 8.9 Cents/kWh = $8.16 per year

 

 

 
PROBLEMS TO SOLVE
 
After school each day, Sally uses her computer to do her homework. If she has an average of two hours of homework per night for 180 days of school per year, how many Kilowatt-hours are consumed and what is the annual cost of using her computer? A CPU and monitor use 270 Watts.
 
 
 
 
Choose a home appliance that you use and calculate your own energy consumption.
 
Appliance: _________________
Wattage: __________________
Hours used Per Day: ________
 
 
You can determine wattage, voltage and current using the following formulas:
wattage = current X voltage
current = wattage/ voltage
voltage = wattage/current
 
Fill in the chart below. The copier has been completed as an example.
 APPLIANCE  VOLTAGE  CURRENT  WATTAGE  COST  HOURS/YEAR  ANNUAL COST
 copier  115V  11A  1265W  $0.08kWh  120  $12.00
 printer  120V  5.5A        
 monitor  120V  2.0A        
 computer  200-240V  3.0A        
 fax machine    1.0A  45W      
 TV  120V    75W      
 microwave  120V    1500W      
 scanner  100-240V  2.0A        
 
 

Lighting Dilemma
 

American homes contain over 3 billion light fixtures. It takes about 138 billion kilowatt-hours of energy per year to operate these lights. 6-10% of our electricity bills are spent on lighting costs. The most common light bulbs in our homes today are incandescent or halogen bulbs. There are also Compact Fluorescent Lights (CFLs). Compact Fluorescent lights contain gas instead of a wire filament. The electric current makes the gas glow, which produces very little heat. CFLs last up to 10 times longer and use 70% less energy. Using energy efficient bulbs can both save money and natural resources.

How much energy/money can be saved by replacing our light bulbs with Compact Fluorescent Lights?

1. Search your home and count the number of lights in each room. Each halogen light uses three times the energy and must be counted three times.
2. Calculate the number of hours the lights are used in each room each day.
3. Enter the data below.

Number of lights Number of hours Lights X hours = TOTAL
Living Room

______________

______________

_____________
Dining Room

______________

_____________

______________
Kitchen

______________

______________

______________
Bedrooms

______________

______________

______________
Bathrooms

______________

______________

______________
Hallways

______________

______________

______________
Family Room

______________

______________

______________
Outside Lights

______________

______________

______________
TOTAL

______________

 

Each energy efficient CFL bulb saves 50 watts, how many watt-hours could you save if you replaced all bulbs with CFLs?

Total hours of operation X 50 watts = _________Watt hours you would save each day

Divide your answer by 1,000 since there are 1,000 watt-hours in a Kilowatt-hour (which is how your utility bills you)

Watt hours / 1,000 = _______________ kilowatt-hours you would save

Take this answer and multiply it by 365 (the days in a year) to calculate the Kilowatt-hours saved in a year.

Kilowatt hours X 365 = __________Kilowatt-hours saved in a year

To calculate the amount of money your family could save in a year, take the Kilowatt-hours saved in a year times the cost per Kilowatt-hour ( in Denver it is $.089).

Kilowatt-hours saved X $.089 = ______________Amount saved per year!

In addition to saving money, we use less electricity! Using less electricity means producing less greenhouse gases. If we assume that every kilowatt-hour saved removes 2 pounds of carbon dioxide from the air, how much greenhouse gases could be prevented?

Kilowatt-hours saved in a year X 2 pounds = _______________pounds of greenhouse gas prevented

 


Reading Electric Meters

Understanding how we use energy can help us better conserve energy. Many different energy sources are used to generate electricity-but more than half of the electricity in the United States is generated by coal-fired power plants. Electricity enters a home through a distribution line that passes through a meter that measures the amount of electricity consumed in kilowatt-hours.

Reading an electric meter is easy. The face of the meter has five dials with the numbers 0-9 on each dial. The dials are not identical though. On the first dial, the numbers increase in a clockwise direction. On the next meter, the numbers increase in the opposite direction, in a counter-clockwise direction. Each dial alternates from clockwsie to counter-clockwise as shown. To read a meter, you read the dials from right to left and record the numbers. If the pointer is between two numbers, you always record the smaller number.


EXAMPLE

Monday morning the meter looked like this:

Friday morning the meter looked like this:

The meter reading Monday would be 40565 and on Friday it would be 41615

To figure out how much electricity was used, subtract Monday's reading from Friday's reading like this:

41,615 - 40,565 = 1,050 kilowatt-hours

Based on electricity costs in Denver of $.089 per kilowatt-hour, the total cost would be: 1,050 X $.089 = $93.45


 

PROBLEM TO SOLVE

On January 1, the meter looked like this:

On January 31, the meter looked like this:

How many kilowatt-hours of electricity were used during January?

If the cost of electricity in Denver is $.089 per kWh, how much did electricity cost for January?

What is the average cost of electricity per day during January?

 

Monitor home energy use by reading the electric meter each morning for a week and determine the cost per week of electricity in your own home.

 

Turn off the power for just one hour. Monitor electricity during a normal hour at home and then turn off as many electrical devices as possible for an hour and record the difference in electrical use.

 


How To Read Utility Bills

Electric companies monitor electric consumption with meters that measure the amount of electricity consumed in buildings. Electricity is measured in kilowatt-hours-kWh. The average cost of electricity in the US is approximately eight cents.

Utilities usually read meters once a month, although some utilities read meters every other month and estimate readings for teh months inbetween. Bills are sent to customers monthly, providing detailed information on the amount of energy consumed and the rate structure for billing.

Many customers can opt for a budget plan, in which they pay the same amount to the utilities each month, regardless of the actual amount of energy they use. This spreads out the seasonal fluctuations in energy use-high heating costs in winter and high cooling costs in summer.

Look at the sample electric bill below. Use the information provided to answer the questions that follow.

 

BUZZ LITE ENERGY COMPANY

 

 DATE

 METER READING
 DECEMBER 1

 970
 DECEMBER 8

 1040
 DECEMBER 15

 1230
DECEMBER 22 

 1410
 DECEMBER 29

 1640
 JANUARY 2

 2260
 JANUARY 9

 2370
 JANUARY 16

 2680
 JANUARY 22

 2920

 

 

1. Using the meter readings from January 9th and December 8th, what was the total kilowatt hour usage?

2. Calculate the actual cost by using the rate schedule. Show your work for each step:

UTILITY RATES:

basic charge(your cost to be connected to the Utility company) ($7.00) +

kWh first 800 ($.06) +

kWh over 800 ($.08) = (your cost) =$ ___________

 

 

Students: Click on the button at the left to connect to the Measurement Worksheet


Created for the NTEP II Fermilab LInC program sponsored by Fermi National Accelerator Laboratory Education Office and Friends of Fermilab, and funded by United States Department of Energy, Illinois State Board of Education, North Central Regional Technology in Education Consortium which is operated by North Central Regional Educational Laboratory (NCREL), and the National Science Foundation.

 

Authors: Sue Emmons, Powell Middle School, Littleton, CO; Kevin Lindauer, John F. Kennedy High School, Denver, CO; Linda Lung, National Renewable Energy Laboratory, Golden, CO; John Sepich, Scott Carpenter Middle School, Westminster, CO; ; Janet Stellema, Monarch K-8, Louisville, CO.
Created: September 9, 1998 - Updated: October 3, 2001.
URL: http://www-ed.fnal.gov/ntep/f98/projects/nrel_energy_2/measurement.html